Organic electroluminescence elements (organic EL elements) are characterized in that they are all-solid-type thin light sources that can operate with a low voltage direct current source. In addition to these characteristics, they also have characteristics that are not seen in other light sources, such as transparency and flexibility.
In an organic EL element, an electrode on the light emitting side generally is an electrode formed of a transparent conductive material such as indium tin oxide (ITO) or zinc oxide (ZnO). By using such a transparent conductive material, it is possible to achieve desired transparency. However, the transparency is in a trade-off relationship with electrical conductivity. That is, while the transparent conductive material is excellent in transparency, it also has high resistivity.
An organic EL element can be produced by forming a first electrode, an organic layer including a light-emitting layer (may be referred to simply as “organic layer” hereinafter), and a second electrode on a transparent substrate in this order, for example. During this process, damage to the organic layer at the time of forming the second electrode is perceived as a problem. The second electrode generally is formed (deposited) by sputtering. Sputtering applies higher energy to a base film during deposition as compared with vapor deposition, and thus may deteriorate the organic layer. However, if the second electrode is formed under the deposition conditions adjusted so as to reduce the damage during the sputtering, it is difficult to allow the second electrode to have a resistivity required in the case where the second electrode is formed on a transparent substrate. Thus, the second electrode has a higher resistivity than the first electrode. Therefore, owing to the influence of voltage drop caused by the resistance of the second electrode, it becomes difficult to obtain uniform light emission over the entire surface.
In order solve the above-described problem, forming an auxiliary wiring layer using a low resistance material such as a metal has been proposed. For example, Patent Document 1 discloses an auxiliary wiring layer (auxiliary electrode) arranged so as to be connected electrically to an electrode. By providing an auxiliary wiring layer formed of a metal having a high electric conductivity together with the electrode as described above, it is possible to alleviate the non-uniformity in light emission.